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    <title>Document</title>
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        let app = new Vue({
            el: "#app",
            data: {
                val: '简单对象初始值',
                obj: {
                    name: "复杂对象name",
                    value: "复杂对象value"
                }
            },
            watch: {
                val: function(newval,oldval){
                    console.log(newval,oldval);
                    console.log(this.val);
                },
                obj: {
                    deep: true,
                    handler: function(new_val,old_val){
                        console.log(new_val,old_val);
                    }
                }
            }
        })
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